techology » Evaporation

Evaporation

techicien — Thu, 22 Apr 2010 09:41:19 +0000

What is Evaporation ?

Evaporation is the removal of solvent as steam from a solution or slurry. For the vast majority of systems of evaporation of the solvent is water. The goal is usually to focus a solution; Consequently, the vapor is not the desired product and can or cannot be retrieved depending on its value. Therefore, evaporation is usually obtained by spraying a portion to produce a concentrated solution, liqueur often or slurry of solvents.

Evaporation often invades denominated transactions distillation, drying and crystallization. In evaporation, no attempt to separate the components of steam. This distinguishes evaporation distillation. Evaporation is distinguished by drying as the residue is always a liquid. The desired product can be a solid, but the heat must be transferred into the evaporator a solution or solid suspension in a liquid. The liquid can be highly viscous or a leachate. Evaporation differs from crystallization in evaporation takes care to concentrate a solution rather than producing or building crystals.

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what an evaporator does

techicien — Tue, 16 Mar 2010 03:01:23 +0000

As mentioned previously, the object of evaporation can be to concentrate a solution containing the desired product or to retrieve the solvent. Sometimes both may be carried out. Design Evaporator consists of three main elements: efficient use of energy, vapor-liquid separation and heat transfer.

In most cases the solvent is water, heat supplied from condensation of steam and the heat is transferred from the indirect heat transfer through metal surfaces. For evaporators be efficient, selected and used equipment must be able to make several things:

1. transfer of large amounts of heat for the solution with a minimum amount of metal surface. This requirement, more than all other factors, determines the type, size and cost of the evaporator.
2. to achieve the specified separation of liquid and vapor and do so with the simplest of devices available. Separation may be important for several reasons: the value of the product otherwise loss; pollution; fouling equipment downstream they contacted the steam; corrosion of this same downstream equipment. Inadequate Separation can also cause problems of pumping or inefficient operation due to undesired recirculation.
3. to make efficient use of energy. This can take many forms. Evaporator performance often are evaluated on the basis of steam economics-pounds of solvent evaporated per pound of steam used. The heat is needed to increase the temperature of the feed from the specified starting value to the boiling liquid, to provide the energy needed to separate the solvent liquid feed and to vaporize solvent. The largest increase in the economy of energy you can reuse the solvent vaporized as heating medium. This may be achieved in various ways to be discussed later. Energy efficiency can be increased for the exchange of heat between the feed enter and leave residues or condensation.
4. meeting the conditions imposed by the liquid is evaporated or solution be concentrated. Factors that should be considered include the quality of the product, Salting and sizing, corrosion, foaming, degradation of the product, holdup, and the need for specific types of construction.
Today many types of evaporators are in use in a wide variety of applications. There is no set rule regarding the selection of types evaporator. In many fields of different types are used in a satisfactory manner for identical services. The final selection and design often can result from tradition or previous experience. The wide variation of the characteristics of the solution expand operation evaporator and design by heat transfer simple A separate art.

Characteristics of liquid

techicien — Sat, 13 Mar 2010 13:12:36 +0000

Concentration

properties of the feed to an evaporator cannot exhibit unusual problems. However, as the liquor is concentrated, can drastically change the properties of the solution. Density and viscosity may increase with solid content until the heat transfer performance is decreased or the solution becomes saturated. Boiling continues a saturated solution can cause form crystals which often must be removed to avoid deficiencies or soil surface heat transfer. The boiling point of a solution increases significantly as is concentrated.

Blowing

Some materials can foam during steaming. Stable Foams may cause excessive swipes. Foaming may be caused by gases dissolved in liquor, from a loss of air under the level of the liquid and the presence of surfactants or finely divided particles in liquor. Many antifoaming agents can be used effectively. Foams can be suppressed by operating at low levels of liquids, mechanically or hydraulic methods.

Temperature sensitivity

many chemicals are compromised when heated to moderate temperatures for relatively short time. When the evaporation of those materials, special techniques are needed to control the characteristics of the time/temperature evaporator system.

Salting

Salting refers to the growth of a matter that a solubility increases with increasing temperature on surfaces evaporator. Can be reduced or eliminated by keeping the evaporation of liquid in close or frequent contacts with a large surface area of solid crystallized.

Scale

scale is growth or deposition on the surfaces of insoluble or heating has a solubility that decreases with increasing temperature. It may also derive from a chemical reaction in the evaporator. Both in scale and salting liquids usually best are handled in a rotary evaporator not based on boiling for operation.

Fouling

Fouling is the formation of deposits several meeting rooms or scale. They may be due to corrosion, solids entering feed or deposits formed by side heating medium.

Corrosion

Corrosion might influence the selection of the type of evaporator because expensive building materials indicate evaporators offering high rates of heat transfer. Corrosion and erosion are often more serious in evaporators compared to other types of equipment for the high speed of liquid and vapor, the frequent presence of suspended solids and concentrations requests.

Quality product

quality may require holdup low and high temperatures. Low-holduptime requirements may eliminate the application of certain types of evaporator. Quality of the product may also dictate special building materials.

Other properties of Fluid

other smooth property must be considered. These include: heat solution, toxicity, explosion hazards, radioactivity and ease of cleaning. Salting, resizing and dirty the result steadily heat transfer speed, until the evaporator must be shut down and cleaned. Some deposits can be difficult and costly to remove.?

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evaporator’s improvement

techicien — Wed, 10 Mar 2010 04:52:47 +0000

Many improvements in technology in the last half century evaporator. The improvements have taken many forms, but have served to do the following:

1. greater evaporation capacity through a better understanding of the mechanisms of heat transfer.
2. better economy through a more efficient use of evaporator types of 3. Longer between cleaning Cycles due to a better understanding of salting, scaling, and smudge.
4. more convenient unit costs from modern production techniques and unit size.
5. to reduce maintenance costs and quality of the product better use of the best materials of construction of better understanding of corrosion.
6. more logical application of specific services evaporator types.
7. a better understanding and application of techniques of control and improvement of instrumentation resulted in better product quality and reduced energy consumption.
8. increased efficiency resulting from heat transfer surfaces more and better energy economy.
9. Compressor technology and availability has allowed for the application of mechanical compression.